The present invention relates to an apparatus for loading an intraluminal device, such as a stent or an embolic device such as a filter, onto the distal end of a catheter assembly similar to those used, for example, in percutaneous transluminal coronary angioplasty (PTCA) procedures or in percutaneous transluminal angioplasty (PTA) procedures. The present invention device is useful in crimping balloon-expandable stents and self-expanding stents.
In typical PTCA procedures, a guiding catheter is percutaneously introduced into the cardiovascular system of a patient through the brachial or femoral arteries and advanced through the vasculature until the distal end of the guiding catheter is in the ostium of the aorta leading to the coronary arteries. A guide wire and a dilatation catheter having a balloon on the distal end are introduced through the guiding catheter with the guide wire sliding within the dilatation catheter. The guide wire is first advanced out of the guiding catheter into the patient""s coronary vasculature and the dilatation catheter is advanced over the previously advanced guide wire until the dilatation balloon is properly positioned across the arterial lesion. Once in position across the lesion, a flexible and expandable balloon is inflated to a predetermined size with a radiopaque liquid at relatively high pressures to radially compress the atherosclerotic plaque of the lesion against the inside of the artery wall and thereby dilate the lumen of the artery. The balloon is then deflated to a small profile so that the dilatation catheter can be withdrawn from the patient""s vasculature and the blood flow resumed through the dilated artery. As should be appreciated by those skilled in the art, while the above-described procedure is typical, it is not the only method used in angioplasty.
In angioplasty procedures of the kind referenced above, restenosis of the artery may develop at or near the treatment area, which may require another angioplasty procedure, a surgical bypass operation, or some other method of repairing or strengthening the area. To reduce the likelihood of the development of restenosis and to strengthen the area, a physician can implant an intravascular prosthesis for maintaining vascular patency, commonly known as a stent, inside the artery at the treated area. The stent is transported in its low profile delivery diameter through the patient""s vasculature. At the deployment site, the stent is expanded to a larger diameter, often by inflating the balloon portion of the catheter. The stent also may be of the self-expanding type.
Since the catheter and stent travel through the patient""s vasculature, and typically through the coronary arteries, the stent must have a small delivery diameter and must be firmly attached to the catheter until the physician is ready to implant it. Thus, the stent must be loaded onto the catheter so that it does not interfere with delivery, and it must not come off the catheter until it is implanted.
In procedures where the stent is placed over the balloon portion of the catheter, it is necessary to crimp the stent onto the balloon portion to reduce its diameter and to prevent it from sliding off the catheter when the catheter is advanced through the patient""s vasculature. Non-uniform crimping can result in sharp edges being formed along the now uneven surface of the crimped stent. Furthermore, non-uniform stent crimping may not achieve the desired minimal profile for the stent and catheter assembly. Where the stent is not reliably crimped onto the catheter, the stent may slide off the catheter and into the patient""s vasculature prematurely as a loose foreign body, possibly causing blood clots in the vasculature, including thrombosis. Therefore, it is important to ensure the proper crimping of a stent onto a catheter in a uniform and reliable manner.
This crimping is sometimes done by hand, which can be unsatisfactory due to the uneven application of force resulting in non-uniform crimps. In addition, it is difficult to visually judge when a uniform and reliable crimp has been applied.
Some self-expanding stents are difficult to load by hand into a delivery device such as a catheter. Self-expanding stents typically are compressed or crimped to a small diameter and then inserted into a delivery catheter where the stent remains until it is pushed out and expands into the vessel. Further, the more the stent is handled the higher the likelihood of human error, which would be antithetical to a properly crimped stent. Accordingly, there is a need in the art for a device for reliably crimping or compressing a self-expanding stent and inserting it into a catheter.
There have been attempts at devising a tool for crimping a stent onto a balloon delivery catheter. An example of such a tool comprises a series of plates having substantially flat and parallel surfaces that move in a rectilinear fashion with respect to each other. A stent carrying catheter is disposed between these surfaces, which surfaces crimp the stent onto the outside of the catheter by their relative motion and applied pressure. The plates have multiple degrees of freedom and may have force-indicating transducers to measure and indicate the force applied to the catheter during crimping of the stent.
Another stent loading tool design is comprised of a tubular member housing a bladder. The tubular member and bladder are constructed to hold a stent that is to be crimped onto a balloon catheter assembly. Upon placement of the stent over the balloon portion of the catheter, a valve in the loading tool is activated to inflate the bladder. The bladder compresses the stent radially inward to a reduced diameter onto the balloon portion of the catheter to achieve a snug fit. In this way, the stent is crimped onto the distal end of a balloon catheter with a minimum of human handling. The foregoing stent crimping tools are disclosed in, for example, commonly owned and assigned U.S. Pat. Nos. 5,437,083 and 5,546,646 to Williams et al.
Yet another stent crimping tool is known in the art as the BARD XT, which is actually a stent loader. It is constructed of a tubular body with a ball at one end connected to a plurality of long, thin strips passing through the rigid tubular body. An uncrimped stent is placed over the plurality of long, thin strips, which hold the stent in an expanded state. The balloon portion of a catheter is inserted into the cylindrical space formed by the plurality of strips. When the user pulls on the ball while holding the tubular body against the stent, the strips are slid from beneath the stent and the stent is transferred onto the balloon portion.
Still another conventional stent crimping tool is manufactured by JOHNSON and JOHNSON and appears similar to a hinged nutcracker. Specifically, the tool is comprised of two hand operated levers hinged at one end and gripped in the palm of the hand at the opposite end. A cylindrical opening holding a crimping tube is provided through the mid-portion of the tool to receive therein a stent loaded onto a balloon catheter. The crimping operation is performed by the user squeezing the handle thereby pressing the crimping tube which in turn pinches the stent onto the balloon catheter.
While the prior art devices are suitable for crimping stents onto balloon catheters, they suffer from problems such as non-uniform crimping forces, resulting in non-uniform crimps, and they are unsuitable for use by physicians in a cath lab who desire to crimp the stent onto the balloon catheter.
The present invention provides for a stent crimping or compressing assembly that is easy to use, and provides a tight and reliable crimped stent onto the distal portion of a stent delivery catheter. Preferably, the stent crimping assembly is used to crimp an expandable stent onto the balloon portion of a catheter, however, the device can be used with self-expanding stents as well. The terms crimping and compressing as used herein are meant to be interchangeable and mean that the diameter of the stent is reduced to some degree. Typically, balloon-expandable stents are known by persons having ordinary skill in the art to be xe2x80x9ccrimpedxe2x80x9d onto the balloon portion of a catheter while self-expanding stents are compressed onto a mandrel or sheath and then inserted into a catheter. Also, references to xe2x80x9cstent crimping assemblyxe2x80x9d as used herein is not meant to be limiting since the assembly can be used as a measuring device to accurately measure the radial strength of a stent. Thus, for ease of reference, the device has been referred to throughout as a stent crimping assembly, but it also is used to measure the radial strength of a stent. Further, while reference is made herein to crimping or compressing xe2x80x9cstents,xe2x80x9d the invention can be used with any intraluminal device to reduce the diameter or measure radial strength. Thus, the invention is particularly useful with stents, grafts, tubular prostheses, embolic devices, embolic filters, and embolic retrieval devices.
In one embodiment, the stent crimping assembly includes a stationary disk that has a front face and a rear face that is mounted on a base. The shaft runs through the center of the stationary disk and is attached to a column that is fixed to the base. A drive disk is configured for rotational movement relative to the stationary disk and it also has a front face and a rear face. The drive disk also is attached to a shaft that is coaxial with the shaft attached to the stationary disk. The rear face of the stationary disk is adjacent to and aligned with the front face of the drive disk. A plurality of linear sliders are attached to the front face of the stationary disk. A plurality of wedges, which have a somewhat triangular face, are attached to the linear sliders and to the drive disk. Each wedge has an apex and two exterior edges that define an exterior angle, wherein each wedge is positioned so that it is substantially equidistant from an adjacent wedge. When the drive disk is rotated, the apex of the wedges move in a direction that is perpendicular to the bisect of the exterior angle and as the apex of each wedge continues to move linearly, the apexes of the wedges move from an open position toward a closed position until the apexes come into crimping contact with a stent that has been premounted on the distal portion of a catheter. As the drive disk continues to rotate, more pressure is applied to the apexes of the sliding wedges so that the stent is firmly crimped onto the distal portion of the catheter. At least three wedges and up to N number of wedges can be provided to uniformly crimp the stent onto the distal end of the catheter. In one embodiment, the wedges are mounted on brackets that are positioned between the wedges and the linear sliders, so that the brackets are attached to both the wedges and the linear sliders. The spacing between the wedges can be varied according to the desired application, but it is an important feature of the invention that there is a spacing between the wedges in order to reduce frictional contact. It should be understood by those skilled in the art that the spacing between the wedges is very small and can depend on the number of wedges used and manufacturing tolerances. References to a xe2x80x9cdiskxe2x80x9d herein are not meant to be limiting and, although the disclosed disks are circular, they can be other shapes without departing from the invention (e.g., square, oval, rectangular). If the drive disk is not circular, however, then the roller bearing should be carried in an arcuate slot (see FIG. 11).
An important aspect of the invention is that the apex of each sliding wedge moves in a linear direction that is substantially perpendicular to the bisect of the exterior angle defined by the edges of the wedge. In other words, the wedges are mounted on linear sliders, and even though the drive disk itself has rotational movement, the wedges must move linearly since they are attached to a linear slider.
A roller bearing or similar device can be used to attach the wedge to the drive disk. The roller bearing is used to minimize the frictional engagement between the sliding wedge and the rotational movement of the drive disk. Other similar attachment means can be provided in place of the roller bearing as long as they minimize the frictional engagement between the sliding wedge and the drive disk.
In one embodiment of the invention, the portion of the assembly including the drive disk and the stationary disk can be rotated a preselected number of degrees N to more uniformly crimp the stent. For example, if eight sliding wedges are used to crimp the stent, under magnification the stent will have the appearance of an octagon. By rotating or indexing the assembly, including the drive disk and stationary disk, and crimping a number of times at a preselected number of degrees N, a more uniformly crimped stent is obtained. For example, in one embodiment the assembly may be rotated 5xc2x0, and the stent then crimped. The assembly is then rotated five more degrees, and the stent crimped again, and so on up to 45xc2x0 rotation in one direction, and 45xc2x0 rotation in the opposite direction. In this manner, the stent will be uniformly crimped and have the appearance, under magnification, of a substantially perfect cylinder.
The rotational force imparted to the drive disk can take any number of forms, including a lever to apply mechanical force, an electric motor, a hydraulic means, and pneumatic means. Further, the amount of force applied by the apex of each wedge onto the stent and the catheter, can be measured and controlled so that the stent and catheter are not damaged while the stent is being tightly crimped onto the catheter.
In one method of crimping the stent onto the catheter, the stent crimping assembly previously described is provided. Rotational movement is imparted to the drive disk which translates to linear movement to the wedges so that the apexes of the wedges form an opening. A stent, that has been premounted on the distal portion of a catheter, is positioned within the opening provided by the apex of the wedges. Rotational movement is imparted to the drive disk which again translates to linear movement to the wedges so that the apexes of the wedges move linearly toward a closed position and into contact with a stent. The stent is crimped onto the catheter by continuing to apply rotational movement to the drive disk and linear movement to the apexes of the wedges toward a closed position and into further crimping contact with the stent. The amount of force applied to the stent can be determined several ways including by force-measuring sensors on the wedges, by the diameter of the opening of the wedges when the stent is crimped or by determining the distance the lever arm moves. After a predetermined amount of force is applied to crimp the stent, the rotational movement to the drive disk is reversed, so that the apexes of the wedges move in a linear direction toward the open position. The crimped stent and catheter are then removed from the crimping assembly.
In one embodiment, the stent crimping device operates as described to crimp a self-expanding stent onto a mandrel. Typically, self-expanding stents are formed of a nickel-titanium alloy that exhibits shape memory effects, superelastic effects, or both. The stent can be cooled by dry ice or other similar cooling means and then mounted on the mandrel where it is tightly crimped onto the mandrel where it is tightly crimped onto the mandrel while it is cooled. The stent is then slipped off of the mandrel and inserted into a catheter for subsequent use to repair a vessel. It may be necessary to place the stent crimping assembly in a chamber so that the chamber can be cooled to a temperature below that which martensite forms so that the stent is more malleable and easily crimped onto the mandrel.
In another embodiment of the invention, the device is used to measure the radial force of a stent. The roller bearing is positioned radially outwardly away from the wedges a sufficient distance so that very little force can be transmitted to the wedges. In this configuration, instead of crimping a stent, an expanded or unexpanded stent is placed in the device with the wedges in the open position. The wedges are moved toward the closed position as previously described and into contact with the stent. The radial force of the stent is measured by continuing to move the wedges toward the closed position. The radial force of the stent is measured by using strain gauges, the geometric position of the wedges, or similar means, to measure the radial resistance of the stent as the wedges continue to move toward the closed position.